Surface-coated cutting tool

ABSTRACT

Provided is a surface-coated cutting tool combining superior heat resistance, superior wear resistance, and superior lubricity. A surface-coated cutting tool of the present invention includes a substrate and a coating formed on the substrate, and the coating is characterized in that the coating is formed by physical vapor deposition and includes one or more layers, that at least one of the one or more layers is a first coating layer, and that the first coating layer contains aluminum and nitrogen, has a thermal effusivity of 2,000 to 5,000 J·sec −1/2 ·m −2 ·K −1 , has a thickness of 0.2 to 5 μm, and has a crystal structure including a hexagonal structure.

TECHNICAL FIELD

The present invention relates to surface-coated cutting tools includingsubstrates and coatings formed on the substrates.

BACKGROUND ART

As a recent trend in cutting tools, the cutting edge temperature of thetools has been becoming increasingly higher for reasons including thedemand for dry machining without the use of a cutting lubricant from theviewpoint of global environmental conservation, diversified workpieces,and increased cutting speeds for higher machining efficiency.Accordingly, the properties required of tool materials have beenbecoming stricter. As the properties required of tool materials,particularly, not only the heat resistance of a coating formed on asubstrate, but also the improvement in wear resistance and thelubrication performance of the coating to replace a lubricant, which arerelated to the lives of cutting tools, have been becoming moreimportant.

For improvements in the heat dissipation, lubricity, and chippingresistance of the coating, a technique is well known that forms acoating of AlN on the surface of a cutting tool formed of a hardsubstrate such as a WC-based cemented carbide, a cermet, or a high-speedsteel. AlN, which has high thermal conductivity, can improve the heatdissipation of the coating and does not trap heat in itself In addition,AlN features high lubricity with low hardness. This feature gives AlNthe advantage of preventing abnormal tool wear and improving thechipping resistance.

Having such various advantages, AlN is almost an essential material forachieving a balance between the lubricity and chipping resistance ofcutting tools at a high level. Accordingly, AlN has been used in variousways. PTL 1, for example, discloses a technique that uses AlN in ahexagonal crystal state for the outermost surface. PTL 2 discloses atechnique that forms a compound layer containing aluminum and one ormore elements selected from the group consisting of nitrogen, oxygen,and carbon by physical vapor deposition. Similarly, PTL 3 discloses atechnique that uses AlN for the surface of a coating. Thus, a coating ofAlN can be formed on the outermost surface to improve the heatdissipation, lubricity, and chipping resistance of that surface.

However, all of the coatings of AlN disclosed in PTL 1 to 3 cause a heatcrack in the tool substrate because they quickly transfer heat generatedduring cutting to the tool substrate (through a lower layer if any) dueto the high thermal effusivity of AlN. This results in the problem of ashortened tool life. In addition, all of the coatings of AlN disclosedin PTL 1 to 3 have an insufficient lubrication effect because they wearquickly due to their insufficient hardness.

As an attempt to further improve the lubricity, on the other hand, PTL 4discloses a technique that adds chlorine to an outermost coating of AlNto improve the lubricity of the outermost surface of the coating. Inaddition, PTL 5 discloses a technique that improves the thermalinsulation and lubricity of the surface of the coating by forming TiCNand TiCNO layers on the substrate side of the coating and forming anAl₂O₃ layer, which has high heat resistance, and an AlN layer, which hashigh lubricity, on the outermost side of the coating.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No.2005-271133

PTL 2: Japanese Unexamined Patent Application Publication No.2005-297143

PTL 3: Japanese Unexamined Patent Application Publication No.2006-026783

PTL 4: Japanese Unexamined Patent Application Publication No.2005-297142

PTL 5: Japanese Unexamined Patent Application Publication No.2003-039210

SUMMARY OF INVENTION Technical Problem

However, none of the techniques in PTL 4 and 5 can solve the problem ofthe low surface hardness of the coating; the outermost surface of thecoating tends to be quickly lost due to wear.

Thus, the technique of improving the lubricity of the surface of thecoating by forming an AlN layer on the surface side of the coating hasoften been used. In addition, an AlN layer formed on the outermost sideof the coating is expected to improve the wear resistance with itslubrication effect; however, a surface-coated cutting tool thatsufficiently exhibits that effect has yet to be provided.

An object of the present invention, which has been made in light of thecurrent circumstances described above, is to provide a surface-coatedcutting tool combining superior heat resistance, superior wearresistance, and superior lubricity by forming a first coating layercontaining aluminum and nitrogen and having low thermal effusivity andhigh hardness on a substrate.

Solution to Problem

A surface-coated cutting tool of the present invention includes asubstrate and a coating formed on the substrate, and the coating ischaracterized in that the coating is formed by physical vapor depositionand includes one or more layers, that at least one of the one or morelayers is a first coating layer, and that the first coating layercontains aluminum and nitrogen, has a thermal effusivity of 2,000 to5,000 J·sec^(−1/2)·m⁻²·K⁻¹, has a thickness of 0.2 to 5 μm, and has acrystal structure including a hexagonal structure.

The first coating layer is preferably an outermost layer of the coating.

The first coating layer preferably has a hardness of 2,500 to 3,800mgf/μm².

The first coating layer preferably has a residual stress of −1 to 0 GPa,and is preferably formed by sputtering.

The first coating layer is preferably formed of Al_(1-x)Me_(x)N(0.001≦x≦0.2), where Me is one or more elements selected from the groupconsisting of vanadium, chromium, yttrium, niobium, hafnium, tantalum,boron, and silicon.

The coating preferably includes one or more second coating layers inaddition to the first coating layer, and the second coating layers arepreferably formed of one or more elements selected from the groupconsisting of group IVa, Va, and VIa elements of the periodic table,aluminum, and silicon, or a compound of one or more of the elements withone or more elements selected from the group consisting of carbon,nitrogen, oxygen, and boron.

One or more of the second coating layers are preferably formed of one ormore elements selected from the group consisting of chromium, aluminum,titanium, and silicon or a compound of one or more of the elements withone or more elements selected from the group consisting of carbon,nitrogen, oxygen, and boron.

The second coating layers preferably have a supermultilayer structureincluding periodically stacked thin-film layers having a thickness of 1to 100 nm, and the thin-film layers are preferably formed of one or moreelements selected from the group consisting of chromium, aluminum,titanium, and silicon or a compound of one or more of the elements withone or more elements selected from the group consisting of carbon,nitrogen, oxygen, and boron.

The substrate is preferably formed of a cemented carbide, a cermet, asintered cubic boron nitride compact, a high-speed steel, a ceramic, ora sintered diamond compact.

Advantageous Effects of Invention

Having the structure described above, the surface-coated cutting tool ofthe present invention has the advantage of combining superior heatresistance, superior wear resistance, and superior lubricity.

DESCRIPTION OF EMBODIMENTS Surface-Coated Cutting Tool

A surface-coated cutting tool of the present invention includes asubstrate and a coating formed thereon. Having that basic structure, thesurface-coated cutting tool of the present invention is significantlyuseful as, for example, a drill, an end mill, an indexable insert formilling or turning, a metal saw, a gear-cutting tool, a reamer, a tap,or an insert for crankshaft pin milling.

Substrate

As the substrate of the surface-coated cutting tool of the presentinvention, any substrate known as a substrate for such cutting tools canbe used. Examples of such substrates include cemented carbides (e.g.,WC-based cemented carbides, which contain cobalt in addition to WC,including those further containing, for example, titanium, tantalum, orniobium carbonitride), cermets (mainly containing, for example, TiC,TiN, or TiCN), high-speed steels, ceramics (e.g., titanium carbide,silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, andmixtures thereof), sintered cubic boron nitride compacts, and sintereddiamond compacts.

If a cemented carbide is used as the substrate, the advantages of thepresent invention are exhibited even if the cemented carbide has freecarbon or an abnormal phase called the η phase in the structure thereofThe substrate may also have the surface thereof modified. For example,if a cemented carbide is used, it may have a β-free layer formed in thesurface thereof, or if a cermet is used, it may have a surface-hardenedlayer formed therein; thus, the advantages of the present invention areexhibited even if the surface is modified.

Coating

The coating of the present invention is characterized in that thecoating is formed by physical vapor deposition, that the coatingincludes one or more layers, that at least one of the one or more layersis a first coating layer, and that the first coating layer containsaluminum and nitrogen, has a thermal effusivity of 2,000 to 5,000J·sec^(−1/2)·m⁻²·K⁻¹, and has a crystal structure including a hexagonalstructure.

Here, the coating of the present invention may be formed such that thecoating covers the entire surface of the substrate, such that thecoating is partially absent, or such that part of the coating is formedin a different manner.

The coating of the present invention preferably has a total thickness of1 to 30 μm. If the thickness of the coating falls below 1 μm, thecoating may have poor wear resistance, whereas if the thickness exceeds30 μm, the coating may be self-destroyed under a compressive stressremaining therein. The preferred thickness of the coating is 2 to 20 μm.

The coating of the present invention is formed by physical vapordeposition (PVD). The reason for employing physical vapor deposition inthe present invention is that it is essential to form a coating having adense structure as the coating formed on the surface of the substrate.Research on various deposition processes has revealed that a coatingformed by physical vapor deposition is best suited.

The individual layers constituting the coating of the present inventionwill now be described in detail.

First Coating Layer

The first coating layer included in the coating of the present inventionis characterized in that it contains aluminum and nitrogen and has athermal effusivity of 2,000 to 5,000 J·sec^(−1/2)·m⁻²·K⁻¹. Knowncoatings containing aluminum and nitrogen are superior in terms oflubricity; however, they have a problem in that their high thermaleffusivity tends to cause the other layers and the substrate to beheated to high temperatures, thus resulting in a shortened tool life dueto heat damage.

The first coating layer of the present invention, which overcomes thedisadvantage of known coatings containing aluminum and nitrogen, canimprove the thermal insulation of known coatings containing aluminum andnitrogen without decreasing the lubricity thereof, thereby preventingthe tool itself from being heated to high temperatures.

If the first coating layer, whose thermal effusivity falls within theabove numerical range, is formed, it can inhibit heat generated duringcutting from being transferred to the tool substrate, thus extending thetool life. The thermal effusivity of the first coating layer ispreferably 3,500 J·sec^(−1/2)·m⁻²·K⁻¹ or less, more preferably 3,000J·sec^(−1/2)·m⁻²·K⁻¹ or less.

If the thermal effusivity of the first coating layer falls below 2,000J·sec^(−1/2)·m⁻²·K⁻¹, it traps excessive heat on the surface sidethereof, thus causing problems such as deformation of AlN crystalsthemselves and decreased hardness. A thermal effusivity exceeding 5,000J·sec^(−1/2)·m⁻²·K⁻¹ is undesirable because the substrate cannot beinsulated from heat generated during cutting and is therefore heated tohigh temperatures, thus suffering deformation or a heat crack.

Here, the value used as the thermal effusivity of the first coatinglayer is a value measured on the basis of thermoreflectance.

The first coating layer of the present invention is characterized inthat it has a total thickness of 0.2 to 5 μm. If the thickness of thefirst coating layer falls below 0.2 μm, the first coating layer may havepoor heat resistance. If the thickness exceeds 5 μm, the first coatinglayer may be self-destroyed under a compressive stress remainingtherein. The preferred thickness of the first coating layer is 0.5 to 2μm.

In addition, the first coating layer is preferably the outermost layerof the coating. That is, the first coating layer is preferably formed onthe outermost surface of the coating opposite the side in contact withthe substrate (hereinafter also referred to as “surface side”). Thus, ifthe first coating layer is formed on the surface side of the coating, itcan improve the heat resistance of the entire tool, thus improving thewear resistance of the surface-coated cutting tool. The hexagonalcrystal structure can be identified by finding a peak attributed to thehexagonal AlN plane in X-ray diffraction (XRD) measurement.

If the first coating layer is formed as the outermost layer, it providessuperior heat resistance and lubrication effect and can also inhibitabnormal wear. Accordingly, the cutting resistance during cutting isreduced. Thus, the surface-coated cutting tool of the present inventioncan significantly effectively prevent the tool itself from beingthermally broken and can also reduce the cutting resistance to providesignificantly superior wear resistance.

The first coating layer preferably has a hardness of 2,500 to 3,800mgf/μm². If a first coating layer having such a high hardness is formed,it improves the wear resistance of the surface-coated cutting tool. Thefirst coating layer more preferably has a hardness of 3,200 to 3,600mgf/μm².

If the hardness of the first coating layer falls below 2,500 mgf/μm²,the coating tends to wear easily because of the insufficient hardness ofthe coating. If the hardness of the first coating layer exceeds 3,800mgf/μm², the coating tends to wear easily because of the decreasedlubricity of the coating. As used herein, the “hardness” refers toindentation hardness, for which a value measured using a nanoindenter(manufactured by Elionix Inc.) is used.

Residual Stress

The first coating layer preferably has a residual stress of −1 to 0 GPa.With such a residual stress, the first coating layer can effectivelyexhibit the property of not being broken during the formation thereof orduring cutting with superior fracture resistance.

Thus, if the residual stress of the entire first coating layer is asmall compressive residual stress, it improves the peeling resistance ofthe coating. In addition, the resistance to breakage due to an impact isimproved. This enhances the effect of extending the tool life. Theresidual stress of the entire first coating layer is more preferably−0.8 to −0.2 GPa.

If the residual stress of the first coating layer falls below −1 GPa,the first coating layer tends to suffer a compressive failure, whereasif the residual stress of the first coating layer exceeds 0 GPa, thecoating tends to be broken upon impact.

Here, the above numerical range of residual stress means that theaverage of the residual stress of the entire first coating layer is −1to 0 GPa. Even if the residual stress of the entire first coating layerdeviates from the above numerical range locally at some positions, itcan improve the peeling resistance and toughness of the coating as longas the average falls within that numerical range.

In addition, the “residual stress” refers to the average residual stressof the entire coating, which can be measured by the sin² ψ method asbelow. The sin² ψ method, which uses X-rays, is widely used as a methodfor measuring the residual stress of polycrystalline materials. Thismeasurement method is described in detail in “X-Sen Oryoku Sokuteiho(X-ray Stress Measurement Method)” (The Society of Materials Science,Japan, published by Yokendo Co., Ltd., 1981), pages 54 to 66. In thepresent invention, first, the depth of penetration of an X-ray is fixedby combining the iso-inclination method and the side-inclination method,and the diffraction angle 2θ is measured in various ψ directions in aplane including the direction of the stress to be measured and thenormal to the surface of the sample at a measurement position to createa 2θ-sin² ψ graph whose gradient is used to determine the average of theresidual stress to that depth (distance from the surface of thecoating).

More specifically, in an X-ray stress measurement method in which anX-ray from an X-ray source is incident on a sample at a predeterminedangle and the X-ray diffracted by the sample is detected by an X-raydetector to measure the internal stress on the basis of the valuedetected, the internal residual stress of the sample (namely, thecoating) can be determined by making the X-ray from the X-ray sourceincident at any position on the surface of the sample at any presetangle and measuring diffraction lines with varying angles ψ between thenormal to the diffraction plane and the normal to the surface of thesample while rotating the sample about the ω axis, which passes throughthe point irradiated with the X-ray on the sample and which isperpendicular to the incident X-ray in the surface of the sample, andabout the χ axis, on which the ω axis coincides with the incident X-rayas the ω axis is rotated parallel to the sample stage, such that theangle between the surface of the sample and the incident X-ray remainsconstant.

The X-ray source used above is preferably synchrotron radiation (SR) interms of the quality of the X-ray source (such as high luminance, highparallelism, and wavelength tunability).

In addition, the Young's modulus and Poisson's ratio of the coating areneeded to determine the residual stress from a 2θ-sin 2ψ graph as above.The Young's modulus can be measured using, for example, a dynamichardness tester. As the Poisson's ratio, which does not vary greatlywith the type of material, a value around 0.2 may be used.

On the other hand, as used herein, the compressive stress (compressiveresidual stress) is a type of internal stress (inherent strain) presentin the coating and is expressed as a negative value (unit: GPa). On theother hand, as used herein, the tensile stress (tensile residual stress)is also a type of internal stress present in the coating and isexpressed as a positive value (unit: GPa). Because the compressivestress and the tensile stress are both internal stresses remaining inthe coating, they are also collectively referred to as the residualstress (including 0 GPa for convenience).

A first coating layer whose residual stress falls within that range canbe formed by adjusting the amount of kinetic energy of atoms or ionsstriking the substrate to form the first coating layer in physical vapordeposition. In general, the larger the amount of kinetic energy, thelarger absolute value the resulting compressive residual stress has. Thedetails of physical vapor deposition will be described later.

Addition of Other Elements

The compound forming the first coating layer of the present invention(i.e., a compound containing aluminum and nitrogen) preferably containsat least one element selected from the group consisting of vanadium,chromium, yttrium, niobium, hafnium, tantalum, boron, and silicon, andthe proportion thereof is preferably 0.1 to 20 atomic percent relativeto the amount of metal component contained in the compound (i.e.,aluminum). That is, the first coating layer is preferably formed ofAl_(1-x)Me_(x)N (0.001≦x≦0.2), where Me is one or more elements selectedfrom the group consisting of vanadium, chromium, yttrium, niobium,hafnium, tantalum, boron, and silicon. If the first coating layercontains such other elements, they strain the crystal structure in thefirst coating layer to further improve the hardness, thus furtherimproving the wear resistance. In addition, these elements inhibitatomic diffusion in the coating or between the coating and the substrateduring cutting to improve the resistance to a reaction such asoxidation.

If the atomic ratio of Me falls below 0.1 atomic percent, the effect ofimproving the hardness is not achieved because the crystal structure inthe first coating layer is not changed. If the atomic ratio of Meexceeds 20 atomic percent, the first coating layer may be self-destroyedbecause the crystal structure in the first coating layer is excessivelystrained.

If the first coating layer is formed by physical vapor deposition usinga target containing such other elements in desired amounts as the sourcematerial of the first coating layer, they can be contained in thecompound forming the layer. The other elements may be contained eitherinterstitially or substitutionally.

Second Coating Layer

In the present invention, the coating preferably includes one or moresecond coating layers in addition to the first coating layer describedabove. The second coating layers may be formed between the substrate andthe first coating layer as an intermediate layer or may be formed on thesurface side of the first coating layer as the outermost layer.

The second coating layers of the present invention preferably have atotal thickness of 1 to 25 μm. If the thickness of the second coatinglayers falls below 1 μm, the second coating layers may have poor wearresistance. If the thickness exceeds 25 μm, the coating may beself-destroyed under a compressive stress remaining in the secondcoating layers. The preferred thickness of the second coating layers is1.8 to 20 μm.

Here, the second coating layers are preferably formed of one or moreelements selected from the group consisting of group IVa, Va, and VIaelements of the periodic table, aluminum, and silicon, or a compound ofone or more of the elements with one or more elements selected from thegroup consisting of carbon, nitrogen, oxygen, and boron. If nitrogen iscontained together with the former elements, the second coating layershave superior toughness and therefore have an advantage in that thecoating is not readily broken when formed as a thick film. If carbon andnitrogen are contained, they can improve the crater resistance. Inaddition, oxygen is preferably contained because it provides superioroxidation resistance and welding resistance. If the second coatinglayers contain aluminum and nitrogen, the second coating layers havesubstantially the same composition as the first coating layer, althoughthey differ from the first coating layer in at least one of thermaleffusivity, thickness, and crystal structure.

The above second coating layers may have either a single-layer structureor a multilayer structure. A multilayer structure is preferable in viewof imparting various functions, and in particular, of multilayerstructures, a supermultilayer structure is more preferable. Here, the“multilayer structure” refers to a multiple layer including two or morelayers, and the “supermultilayer structure” refers to a stack of about100 to 10,000 layers of two or more types having different propertiesand compositions, each having a thickness of several nanometers toseveral hundreds of nanometers (typically, stacked alternately orrepeatedly on top of each other).

One or more of the second coating layers are preferably formed of one ormore elements selected from the group consisting of chromium, aluminum,titanium, and silicon or a compound of one or more of the elements withone or more elements selected from the group consisting of carbon,nitrogen, oxygen, and boron.

The second coating layers preferably have a supermultilayer structureincluding periodically stacked thin-film layers having a thickness of 1to 100 nm. The thin-film layers are more preferably formed of one ormore elements selected from the group consisting of chromium, aluminum,titanium, and silicon or a compound of one or more of the elements withone or more elements selected from the group consisting of carbon,nitrogen, oxygen, and boron. If the second coating layers have asupermultilayer structure, the deposition rate is higher becausedifferent targets are used and the thickness of the layers is on theorder of several nanometers. In addition, layers having differentproperties and compositions can be combined to improve the filmproperties, including the hardness, thermal insulation, oxidationresistance, and toughness of the coating.

Production Process

As the physical vapor deposition (PVD) process used for forming thecoating of the present invention, any known physical vapor depositionprocess can be used. It is essential to use a deposition process thatallows formation of a highly crystalline compound in order to depositthe coating of the present invention on the surface of the substrate.Research on various deposition processes has revealed that the use ofphysical vapor deposition is best suited. Examples of physical vapordeposition processes include sputtering, ion plating, arc ion plating,and electron/ion beam deposition; in particular, cathode arc ionplating, where the source elements are ionized at a high rate, orsputtering is preferably used because they provide high productivity.

Among physical vapor deposition processes, the first coating layer ispreferably formed by sputtering. If the first coating layer is formed bysputtering, the first coating layer has a homogeneous crystal structure.This provides the advantage of increasing the hardness of the firstcoating layer. The specific conditions for sputtering are exemplified asfollows.

Specifically, pulsed sputtering is used for alternate application ofhigh-frequency pulses and low-frequency pulses. The target used is asintered or fused target having the target composition. A pulsefrequency of 100 kHz or less and a pulse frequency of 300 kHz or moreare alternately applied to the sputter cathode by controlling the pulsefrequency each time a thickness of 20 to 70 nm is reached.

In this way, varying pulse frequencies can be alternately applied toadjust the energy of particles coming from the target. That is, as theproportion of a pulse frequency of 300 kHz or more is increased, thecrystals of the first coating layer grow more three-dimensionally, andaccordingly the hardness increases; as the proportion of a pulsefrequency of 100 kHz or less is increased, the growth of the crystals ofthe first coating layer is retarded, and accordingly the hardness tendsto decrease. Thus, these pulse frequencies can be appropriatelycontrolled to retard the crystal growth of the first coating layer whilekeeping it highly crystalline, thus forming a first coating layer with auniform crystal structure.

When the pulse frequency applied to the sputter cathode is controlled to100 kHz or less, the bias applied to the substrate preferably has afrequency of 200 kHz or more and a bias voltage to 50 V or more. Whenthe pulse frequency applied to the sputter cathode is controlled to 300kHz or more, the bias applied to the substrate preferably has afrequency of 100 kHz or less and a bias voltage to less than 50 V. Inthis way, the bias applied to the substrate can be adjusted to form afirst coating layer with a dense crystal structure, thus improving thethermal insulation of the coating.

EXAMPLES

The present invention will be described in more detail with reference tothe examples below, although the invention is not limited thereto. Thethickness of the coatings and the individual layers in the examples wasmeasured by examining cross sections of the coatings using a scanningelectron microscope (SEM) or a transmission electron microscope (TEM),and the composition of the compounds forming the individual layers inthe examples was examined by X-ray photoelectron spectroscopy (XPS). Inaddition, the crystal structure was examined by X-ray diffraction (XRD),where the measurement was carried out at an incident angle of 0.5°. Inaddition, the residual stress of the entire coatings was measured by thesin² ψ method described above, and the hardness was measured using ananoindenter (manufactured by Elionix Inc.). Furthermore, the thermaleffusivity was measured by thermoreflectance in an environment with atest temperature of 24° C. and a test humidity of 30% using a thermalmicroscope (Thermal Microscope TM3 (manufactured by BETHEL Co., Ltd.))in the point measurement mode in combination with a detection laserhaving a measurement frequency of 3 MHz.

Examples 1 to 56 and Comparative Examples 1 to 14

Surface-coated cutting tools were produced and evaluated as follows.

Production of Surface-Coated Cutting Tools

In Examples 1 to 28 and Comparative Examples 1 to 7, first, assubstrates of surface-coated cutting tools for face milling, substratesformed of a P20 cemented carbide and having the shape of SDEX42MT (JIS)were prepared. As substrates of surface-coated cutting tools forturning, substrates formed of a P20 cemented carbide and having theshape of CNMG120408 (JIS) were prepared. These substrates were set to acathode arc ion plating/sputtering apparatus.

In Examples 29 to 56 and Comparative Examples 8 to 14, on the otherhand, as substrates of surface-coated cutting tools for face milling,substrates formed of a P20 cemented carbide and having the shape ofSEET13T3AGSN (JIS) were prepared. As substrates of surface-coatedcutting tools for turning, substrates formed of a K20 cemented carbideand having the shape of CNMG120408 (JIS) were prepared. These substrateswere set to a cathode arc ion plating/sputtering apparatus or CVDapparatus.

Subsequently, the internal pressure of a chamber of the apparatus wasreduced by a vacuum pump while the substrate temperature was raised to600° C. by a heater installed in the apparatus, the chamber beingevacuated until the internal pressure was reduced to 1.0×10⁻⁴ Pa.

Next, the surfaces of the substrates were cleaned for 30 minutes bygradually raising the voltage of the substrate bias power supply for thesubstrates to −1,500 V to heat a tungsten filament so that it emittedthermal electrons while introducing argon gas into the chamber so as tomaintain the internal pressure at 3.0 Pa. The argon gas was dischargedthereafter. Then, the intermediate layers shown in Tables I to IV wereformed directly on the substrates in the order of the first, second, andthird layers. The symbol “-” in the tables means that no correspondinglayer was formed. The intermediate layers were deposited by a knownmethod using sintered or fused targets having the target compositions,that is, the metal compositions of the intermediate layers shown inTables I to IV, while introducing Ar, N₂, CH₄, and O₂ gases.

TABLE I Intermediate layer First coating layer First layer Second layerThermal Thickness Thickness Production effusivity Crystal Composition(μm) Composition (μm) Composition process (J · sec⁻¹ · m⁻¹ · K⁻¹)structure Example 1 Ti_(0.5)Al_(0.5)N 3 — — AlN AlP 4800 Hexagonal 2Ti_(0.5)Al_(0.5)N 3 — — AlN AlP 4200 Hexagonal 3 Ti_(0.5)Al_(0.5)N 3 — —AlN SP 3500 Hexagonal 4 Ti_(0.5)Al_(0.5)N 3 — — AlN SP 3200 Hexagonal 5Ti_(0.5)Al_(0.5)N 3 — — AlN SP 3100 Hexagonal 6 Ti_(0.5)Al_(0.5)N 3 — —AlN SP 2700 Hexagonal 7 Ti_(0.5)Al_(0.5)N 3 — — AlN SP 2500 Hexagonal 8Ti_(0.5)Al_(0.5)N 3 — — AlN SP 2400 Hexagonal 9 Ti_(0.5)Al_(0.5)N 3 — —AlN SP 2100 Hexagonal 10 Ti_(0.5)Al_(0.5)N 3 — — AlN SP 2400 Hexagonal11 Ti_(0.5)Al_(0.5)N 3 — — AlN SP 2400 Hexagonal 12 Ti_(0.5)Al_(0.5)N 3— — AlN SP 2400 Hexagonal 13 Ti_(0.5)Al_(0.5)N 3 — — AlN SP 2400Hexagonal 14 Ti_(0.5)Al_(0.5)N 3 — — Al_(0.94)Cr_(0.06)N SP 2600Hexagonal 15 Ti_(0.5)Al_(0.5)N 3 — — Al_(0.98)V_(0.02)N SP 2200Hexagonal 16 Ti_(0.5)Al_(0.5)N 3 — — Al_(0.97)V_(0.03)N SP 2400Hexagonal 17 Ti_(0.5)Al_(0.5)N 3 — — Al_(0.95)Si_(0.05)N SP 2000Hexagonal 18 Ti_(0.5)Al_(0.5)N 3 — — Al_(0.92)Ta_(0.08)N SP 2400Hexagonal 19 Ti_(0.5)Al_(0.5)N 3 — — Al_(0.99)Hf_(0.01)N SP 2300Hexagonal 20 Ti_(0.5)Al_(0.5)N 3 — — Al_(0.03)Y_(0.07)N SP 2100Hexagonal 21 Ti_(0.5)Al_(0.5)N 3 — — Al_(0.93)B_(0.07)N SP 2400Hexagonal 22 TiN 0.5 Ti_(0.9)Si_(0.07)N 2.5 AlN SP 2100 Hexagonal 23Ti_(0.5)Al_(0.5)N 0.5 Al_(0.7)Cr_(0.3)N 2.5 AlN SP 2000 Hexagonal 24 TiN0.3 Al_(0.47)Cr_(0.45)Si_(0.08)N 2.5 AlN SP 2100 Hexagonal 25Ti_(0.5)Al_(0.5)N 0.5 Ti_(0.3)Al_(0.7)N (8 nm)/ 2.5 AlN SP 2100Hexagonal TiN(7 nm) 26 Ti_(0.5)Al_(0.5)N 0.5 Ti_(0.5)Al_(0.5)N (6 nm)/2.5 AlN SP 2100 Hexagonal Al_(0.7)Cr_(0.3)N (7 nm) 27 TiN 0.3Ti_(0.47)Al_(0.47)Si_(0.05)N (7 nm) 2.5 AlN SP 2100 Hexagonal 28 TiN 0.3Ti_(0.47)Al_(0.47)Si_(0.05)N (7 nm) 2.5 Al_(0.93)Cr_(0.07)N SP 2500Hexagonal First coating layer Outermost layer Residual First layerSecond layer Total Thickness Hardness stress Thickness Thicknessthickness (μm) (mgf/μm) (GPa) Composition (μm) Composition (μm) (μm)Example 1 1.3 1800 −1.5 TiN 0.2 — — 4.5 2 1.2 2000 −0.9 TiN 0.2 — — 4.43 1.1 2500 −0.8 TiN 0.2 — — 4.3 4 0.9 2800 −0.1 TiN 0.2 — — 4.1 5 1 3000−0.6 TiN 0.2 — — 4.2 6 1.3 3200 −0.5 TiN 0.2 — — 4.5 7 1.3 3700 −0.2 TiN0.2 — — 4.5 8 1 3300 −0.4 TiN 0.2 TiCN 0.1 4.3 9 1.2 3500 −0.6 TiN 0.2TiCN 0.1 4.5 10 1.9 3300 −0.4 TiN 0.2 TiCN 0.1 5.2 11 2.4 3300 −0.3 TiN0.2 TiCN 0.1 5.7 12 4 3300 −0.6 TiN 0.2 — — 7.2 13 4.8 3300 −0.4 TiN 0.2— — 8 14 0.9 3600 −0.4 TiN 0.2 — — 4.1 15 1.1 3300 −0.4 TiN 0.2 — — 4.316 1.1 3400 −0.4 TiN 0.2 — — 4.3 17 1 3000 −0.4 TiN 0.2 — — 4.2 18 1.23300 −0.4 TiN 0.2 — — 4.4 19 1 3200 −0.4 TiN 0.2 — — 4.2 20 1 3000 −0.4TiN 0.2 — — 4.2 21 1.1 2800 −0.4 TiN 0.2 — — 4.3 22 1.2 3500 −0.6 TiN0.2 TiCN 0.1 4.5 23 1.2 3500 −0.6 TiN 0.2 TiCN 0.1 4.5 24 1.2 3600 −0.6TiN 0.2 TiCN 0.1 4.3 25 1.2 3500 −0.6 TiN 0.2 TiCN 0.1 4.5 26 1.2 3400−0.3 TiN 0.2 TiCN 0.1 4.5 27 1.2 3600 −0.7 TiN 0.2 TiCN 0.1 4.3 28 13200 −0.4 TiN 0.2 TiCN 0.1 4.1

TABLE II Outermost Intermediate layer First coating layer layer TotalCom- Thick- Com- Produc- Thick- Residual Com- Thick- thick- po- ness po-tion Thermal effusivity Crystal ness Hardness stress po- ness nesssition (μm) sition process (J · sec⁻¹ · m⁻¹ · K⁻¹) structure (μm)(mgf/μm) (Gpa) sition (μm) (μm) Com- 1 Ti_(0.5)Al_(0.5)N 3 AlN AlP 7500Hexagonal 1.2 1700 −1.4 TiN 0.2 4.4 par- 2 Ti_(0.5)Al_(0.5)N 3 AlN CVD8700 Hexagonal 1.1 1400 0.2 TiN 0.2 4.3 ative 3 Ti_(0.5)Al_(0.5)N 3 AlNSP 1600 Hexagonal 0.8 1600 −0.6 TiN 0.2 4 exam- 4 Ti_(0.5)Al_(0.5)N 3AlN SP 5200 Hexagonal 0.8 4000 −1.2 TiN 0.2 4 ple 5 Ti_(0.5)Al_(0.5)N 3AlN SP 2500 Hexagonal 5.5 3600 −0.2 TiN 0.2 8.7 6 Ti_(0.5)Al_(0.5)N 3AlN SP 2500 Hexagonal 0.1 3600 −0.2 TiN 0.2 3.3 7 Ti_(0.5)Al_(0.5)N 3AlN SP 1400 Amorphous 1.3 1800 −0.1 TiN 0.2 4.5

TABLE III Intermediate layer First layer Second layer Third layerThickness Thickness Thickness Composition (μm) Composition (μm)Composition (μm) Example 29 Ti_(0.5)Al_(0.5)N 3 — — — — 30Ti_(0.5)Al_(0.5)N 3 — — — — 31 Ti_(0.5)Al_(0.5)N 3 — — — — 32Ti_(0.5)Al_(0.5)N 3 — — — — 33 Ti_(0.5)Al_(0.5)N 3 — — — — 34Ti_(0.5)Al_(0.5)N 0.4 Al_(0.7)Cr_(0.3)N 3.5 — — 35 Ti_(0.6)Al_(0.4)N 0.5Ti_(0.45)Al_(0.48)Si_(0.07)N 3.5 — — 36 TiN 0.5 Ti_(0.3)Al_(0.7)N 3.5 —— 37 Ti_(0.5)Al_(0.5)N 0.5 Ti_(0.45)Al_(0.48)Si_(0.07)N 3.5 — — 38Ti_(0.5)Al_(0.5)N 0.5 Al_(0.7)Cr_(0.3)N 2.5 Ti_(0.9)Si_(0.1)CN 1   39Ti_(0.6)Al_(0.4)N 0.5 Ti_(0.45)Al_(0.48)Si_(0.07)N 3.5 — — 40Ti_(0.6)Al_(0.4)N 0.5 Ti_(0.45)Al_(0.48)Si_(0.07)N 3.5 — — 41Ti_(0.6)Al_(0.4)N 0.5 Ti_(0.45)Al_(0.48)Si_(0.07)N 3.5 — — 42Ti_(0.6)Al_(0.4)N 0.5 Ti_(0.45)Al_(0.48)Si_(0.07)N 3.5 — — 43Ti_(0.6)Al_(0.4)N 0.5 Ti_(0.4)Al_(0.44)Cr_(0.08)Si_(0.08)N 3.5 — — 44Ti_(0.6)Al_(0.4)N 0.5 Ti_(0.45)Al_(0.48)Si_(0.07)N 3.5 — — 45Ti_(0.6)Al_(0.4)N 0.5 Ti_(0.45)Al_(0.48)Si_(0.07)N 3.5 — — 46Ti_(0.6)Al_(0.4)N 0.5 Ti_(0.45)Al_(0.48)Si_(0.07)N 3.5 — — 47Ti_(0.6)Al_(0.4)N 0.5 Ti_(0.45)Al_(0.48)Si_(0.07)N 3.5 — — 48Ti_(0.6)Al_(0.4)N 0.5 Ti_(0.45)Al_(0.48)Si_(0.07)N 3.5 — — 49Ti_(0.6)Al_(0.4)N 0.5 Ti_(0.45)Al_(0.48)Si_(0.07)N 3.5 — — 50Ti_(0.6)Al_(0.4)N 0.5 Ti_(0.45)Al_(0.48)Si_(0.07)N 3.5 — — 51Ti_(0.6)Al_(0.4)N 0.5 Ti_(0.45)Al_(0.48)Si_(0.07)N 3.5 — — 52Ti_(0.6)Al_(0.4)N 0.5 Ti_(0.45)Al_(0.48)Si_(0.07)N 2.5 Al₂O₃ 0.7 53 TiN0.5 Al_(0.7)Cr_(0.3)N 3 Al_(0.97)Cr_(0.03)NO 0.3 54 Ti_(0.6)Al_(0.4)N0.5 Ti_(0.93)Si_(0.07)N (8 nm)/ 3.5 — — Ti_(0.45)Al_(0.48)Si_(0.07)N (11nm) 55 Ti_(0.6)Al_(0.4)N 0.5 TiN (7 nm)/ 3.5 — —Ti_(0.4)Al_(0.48)Si_(0.07)Cr_(0.05)N (6 nm) 56 Ti_(0.6)Al_(0.4)N 0.5 TiN(7 nm)/ 3.5 — — Ti_(0.45)Al_(0.48)Si_(0.07)N (5 nm)/Al_(0.48)Cr_(0.45)Si_(0.07)N (5 nm) First coating layer Thermal Produc-effusivity Thick- Residual Total tion (J · sec⁻¹ · Crystal ness Hardnessstress thickness Composition process m⁻¹ · K⁻¹) structure (μm) (mgf/μm)(GPa) (μm) Example 29 AlN AlP 5000 Hexagonal 1 1600 −1.6 4 30 AlN SP4700 Hexagonal 1 2200 −0.8 4 31 AlN SP 4200 Hexagonal 0.8 3400 −0.2 3.832 AlN SP 3500 Hexagonal 0.9 3300 −0.6 3.9 33 AlN SP 3300 Hexagonal 1.23400 −0.7 4.2 34 AlN SP 3000 Hexagonal 1 3200 −0.2 4.9 35 AlN SP 2700Hexagonal 0.7 3400 −0.4 4.7 36 AlN SP 2600 Hexagonal 0.7 2700 −0.6 4.737 AlN SP 2100 Hexagonal 1.1 3600 −0.5 5.1 38 AlN SP 2000 Hexagonal 13500 −0.2 5 39 AlN SP 2300 Hexagonal 0.2 3600 −0.7 4.2 40 AlN SP 2100Hexagonal 1.5 3600 −0.3 5.5 41 AlN SP 2100 Hexagonal 1.9 3500 −0.2 5.942 AlN SP 2300 Hexagonal 3 3500 −0.2 7 43 AlN SP 2100 Hexagonal 3.7 3600−0.2 7.7 44 AlN SP 2000 Hexagonal 4.9 3600 −0.3 8.9 45Al_(0.93)Cr_(0.07)N SP 3400 Hexagonal 1 2900 −0.4 5 46Al_(0.93)B_(0.07)N SP 2400 Hexagonal 1 3000 −0.2 5 47 Al_(0.04)V_(0.06)NSP 3000 Hexagonal 0.9 3000 −0.6 4.9 48 Al_(0.95)Si_(0.05)N SP 2300Hexagonal 1 3600 −0.2 5 49 Al_(0.92)Ta_(0.08)N SP 2200 Hexagonal 1 3100−0.2 5 50 Al_(0.98)Hf_(0.02)N SP 3100 Hexagonal 1.2 2900 −0.5 5.2 51Al_(0.93)Y_(0.07)N SP 2700 Hexagonal 1 3200 −0.5 5 52 AlN SP 2200Hexagonal 1 3100 −0.2 4.7 53 AlN SP 2200 Hexagonal 1 3100 −0.2 5 54 AlNSP 2200 Hexagonal 1 3100 −0.2 5 55 AlN SP 2200 Hexagonal 1 3100 −0.2 556 AlN SP 2200 Hexagonal 1 3100 −0.2 5

TABLE IV First coating layer Intermediate layer Thermal Outermost layerTotal Thick- Com- Produc- effusivity Thick- Residual Thick- thick- nessposi- tion (J · sec⁻¹ · Crystal ness Hardness stress ness nessComposition (μm) tion process m⁻¹ · K⁻¹) structure (μm) (mgf/μm) (Gpa)Composition (μm) (μm) Compar- 8 Ti_(0.5)Al_(0.5)N 3 AlN SP 4700Hexagonal 1 2200 −0.8 Ti_(0.94)Hf_(0.06)CN 1.5 5.5 ative 9Ti_(0.5)Al_(0.5)N 3 AlN SP 1800 Hexagonal 1 3000 −0.2 — — 4 example 10Ti_(0.5)Al_(0.5)N 3 AlN SP 5200 Hexagonal 1 1700 −0.2 — — 4 11Ti_(0.5)Al_(0.5)N 3 AlN CVD 5500 Hexagonal 1 5700 −0.3 — — 4 12Ti_(0.5)Al_(0.5)N 3 AlN SP 1200 Amorphous 1 4900 −0.1 — — 4 13Ti_(0.5)Al_(0.5)N 3 AlN SP 4700 Hexagonal 5.5 1900 −0.1 — — 8.5 14Ti_(0.5)Al_(0.5)N 3 AlN SP 4700 Hexagonal 0.1 2200 −0.9 — — 3.1

In Tables I to IV, the “composition” in the columns “first layer,”“second layer,” and “third layer” shows the compositions of the secondcoating layers forming the respective layers, and the “thickness” showsthe thicknesses of the respective layers. In addition, the second layersof Examples 25 to 28 in Table I and the second layers of Examples 54 to56 in Table III, which had a supermultilayer structure, were depositedunder known conditions to the thicknesses shown in parentheses besidethe compositions.

Subsequently, the first coating layers shown in Tables I to IV wereformed on the intermediate layers formed as above. The first coatinglayers were formed so as to have the thicknesses shown in Tables I to IVusing sintered or fused targets having the target compositions, that is,the metal compositions of the first coating layers shown in Tables I toIV, while introducing Ar and N₂.

In Tables I to IV, the “composition” in the column “first coating layer”shows the compositions of the compounds forming the first coatinglayers. The “AlN,” for example, in Tables I to IV refers to acrystalline or amorphous material composed of aluminum and nitrogen,where the atomic ratio of aluminum to nitrogen is not limited to 1:1,but may deviate slightly therefrom and includes all known atomic ratios;that is, their atomic ratio is not particularly limited. As in the caseof AlN above, none of the compositions shown in Tables I to IV islimited in composition ratio.

Furthermore, the “AIP” in the column “production process” indicates thatthe layer was formed by arc ion plating, the “SP” indicates that thelayer was formed by sputtering, and the “CVD” indicates that the layerwas formed by a known chemical vapor deposition process. In addition,the column “thickness” shows the thicknesses of the first coatinglayers. In addition, the column “hardness” shows the indentationhardnesses measured using a nanoindenter hardness tester, and the column“residual stress” shows the average residual stresses of the entirefirst coating layers.

For the formation of the first coating layer by sputtering, it wasformed by raising the deposition temperature to 500° C. and alternatelyapplying a pulse frequency of 100 kHz or less and a pulse frequency of300 kHz or more to the sputter cathode by controlling the pulsefrequency each time a thickness of 20 to 70 nm was reached.

To form a dense crystal structure in the first coating layer, the pulsefrequency and bias with which the first coating layer was formed wereadjusted. Specifically, when the pulse frequency applied to the sputtercathode was controlled to 100 kHz or less, the bias applied to thesubstrate was adjusted to a frequency of 200 kHz or more and a biasvoltage of 50 V or more, whereas when the pulse frequency applied to thesputter cathode was controlled to 300 kHz or more, the bias applied tothe substrate was adjusted to a frequency of 100 kHz or less and a biasvoltage of less than 50 V. The sputter power was adjusted so that thedeposition rate was 0.1 to 0.6 μm/h.

Subsequently, the outermost layers shown in Tables I, II, and IV wereformed on the first coating layers formed as above. In the tables, thesymbol “-” in the column showing the compositions of the outermostlayers means that no outermost layer was formed. The outermost layers,which can be formed in the same manner as the second coating layersdescribed above, were deposited by a known method using sintered orfused targets having the target compositions, that is, the metalcompositions of the outermost layers shown in Tables I, II, and IV, soas to have the thicknesses shown in Tables I, II, and IV.

In Tables I, II, and IV, the “composition” in the column “outermostlayer” shows the compositions of the compounds forming the outermostlayers, and the column “total thickness” shows the thicknesses of theentire coatings.

Wear Resistance Evaluation of Surface-Coated Cutting Tools

The surface-coated cutting tools, produced as above, of Examples 1 to 56and Comparative Examples 1 to 14 were each evaluated for wear resistanceby a face milling test and a continuous turning test under the followingconditions. The evaluation was carried out by measuring, as the cuttingtime, the time elapsed before the width of flank wear at the cuttingedge exceeded 0.2 mm or the time elapsed before the coating fractured.For both the face milling test and the continuous turning test, a longercutting time indicates superior wear resistance. Examples 1 to 28 andComparative Examples 1 to 7 and Examples 29 to 56 and ComparativeExamples 8 to 14 were evaluated for wear resistance under differentconditions, the details of which will be described below. The resultsare shown in Tables V and VI.

Conditions for Face Milling Test

In Examples 1 to 28 and Comparative Examples 1 to 7, as the substrates,as described above, the face milling indexable inserts formed of a P20cemented carbide and having the shape of SDEX42MT (JIS) were subjectedto the test under the following conditions:

Workpiece: SCM435 (size of machined surface: 300 mm×120 mm)

Cutting speed: 230 m/min

Depth of cut: 2.0 mm

Feed: 0.2 mm/rev

Dry/wet: dry

In Examples 29 to 56 and Comparative Examples 8 to 14, on the otherhand, as the substrates, as described above, the face milling indexableinserts formed of a P20 cemented carbide and having the shape ofSEET13T3AGSN (JIS) were subjected to the test under the followingconditions:

Workpiece: SCM435 (size of machined surface: 300 mm×120 mm)

Cutting speed: 300 m/min

Depth of cut: 2.0 mm

Feed: 0.2 mm/rev

Dry/wet: dry

Conditions for Continuous Turning Test

In Examples 1 to 28 and Comparative Examples 1 to 7, as the substrates,as described above, the turning indexable inserts formed of a P20cemented carbide and having the shape of CNMG120408 were subjected tothe test under the following conditions:

Workpiece: SCM435 round bar

Cutting speed: 200 m/min

Depth of cut: 2.0 mm

Feed: 0.2 mm/rev

Dry/wet: wet

In Examples 29 to 56 and Comparative Examples 8 to 14, as thesubstrates, as described above, the turning indexable inserts formed ofa K20 cemented carbide and having the shape of CNMG120408 were subjectedto the test under the following conditions:

Workpiece: Inconel 718 round bar

Cutting speed: 70 m/min

Depth of cut: 0.5 mm

Feed: 0.15 mm/rev

Dry/wet: wet

TABLE V Life Face milling Turning Example 1 31 min. 50 sec. 18 min. 8sec. 2 33 min. 37 sec. 17 min. 31 sec. 3 36 min. 59 sec. 20 min. 24 sec.4 37 min. 5 sec. 21 min. 31 sec. 5 40 min. 46 sec. 23 min. 49 sec. 6 43min. 4 sec. 25 min. 26 sec. 7 41 min. 42 sec. 24 min. 28 sec. 8 44 min.16 sec. 25 min. 48 sec. 9 43 min. 57 sec. 26 min. 46 sec. 10 42 min. 15sec. 24 min. 45 sec. 11 41 min. 2 sec. 24 min. 50 sec. 12 40 min. 48sec. 23 min. 17 sec. 13 40 min. 6 sec. 23 min. 31 sec. 14 48 min. 41sec. 28 min. 22 sec. 15 45 min. 10 sec. 26 min. 11 sec. 16 45 min. 31sec. 26 min. 44 sec. 17 46 min. 12 sec. 27 min. 59 sec. 18 46 min. 15sec. 27 min. 14 sec. 19 48 min. 27 sec. 28 min. 29 sec. 20 46 min. 55sec. 26 min. 48 sec. 21 48 min. 7 sec. 28 min. 50 sec. 22 42 min. 41sec. 24 min. 43 sec. 23 43 min. 27 sec. 25 min. 40 sec. 24 42 min. 24sec. 24 min. 4 sec. 25 50 min. 11 sec. 29 min. 39 sec. 26 52 min. 51sec. 32 min. 37 sec. 27 52 min. 46 sec. 31 min. 31 sec. 28 51 min. 12sec. 30 min. 7 sec. Comparative 1 15 min. 43 sec.  7 min. 34 sec.example 2 13 min. 8 sec.  4 min. 47 sec. 3 19 min. 16 sec. 10 min. 13sec. 4 17 min. 53 sec.  8 min. 39 sec. 5 22 min. 32 sec. 12 min. 10 sec.6 20 min. 13 sec. 12 min. 26 sec. 7 13 min. 19 sec.  5 min. 31 sec.

TABLE VI Life Face milling Turning Example 29 12 min. 51 sec. 24 min. 46sec. 30 12 min. 48 sec. 28 min. 37 sec. 31 14 min. 19 sec. 30 min. 45sec. 32 17 min. 29 sec. 35 min. 52 sec. 33 18 min. 9 sec. 33 min. 23sec. 34 19 min. 4 sec. 34 min. 16 sec. 35 20 min. 3 sec. 35 min. 3 sec.36 14 min. 16 sec. 30 min. 58 sec. 37 18 min. 56 sec. 33 min. 25 sec. 3818 min. 8 sec. 33 min. 18 sec. 39 17 min. 52 sec. 31 min. 41 sec. 40 18min. 54 sec. 33 min. 22 sec. 41 17 min. 34ec. 32 min. 17 sec. 42 16 min.46 sec. 30 min. 23 sec. 43 15 min. 33 sec. 29 min. 24 sec. 44 15 min. 5sec. 28 min. 43 sec. 45 21 min. 21 sec. 36 min. 1 sec. 46 21 min. 44sec. 36 min. 51 sec. 47 21 min. 40 sec. 36 min. 19 sec. 48 22 min. 17sec. 38 min. 6 sec. 49 21 min. 48 sec. 35 min. 47 sec. 50 21 min. 35sec. 37 min. 8 sec. 51 22 min. 34 sec. 38 min. 14 sec. 52 15 min. 27sec. 30 min. 34 sec. 53 14 min. 18 sec. 30 min. 54 sec. 54 24 min. 3sec. 39 min. 35 sec. 55 25 min. 52 sec. 41 min. 47 sec. 56 27 min. 45sec. 40 min. 30 sec. Comparative 8  7 min. 58 sec. 12 min. 10 sec.example 9  6 min. 6 sec. 11 min. 44 sec. 10  5 min. 50 sec. 10 min. 53sec. 11 36 sec.  5 min. 15 sec. 12  6 min. 30 sec.  8 min. 16 sec. 13  2min. 26 sec.  8 min. 34 sec. 14  6 min. 31 sec. 11 min. 9 sec.

As is obvious from Table V, the surface-coated cutting tools of Examples1 to 28 according to the present invention had a higher wear resistancethan the surface-coated cutting tools of Comparative Examples 1 to 7,demonstrating that the tool life was improved.

Similarly, as is obvious from Table VI, the surface-coated cutting toolsof Examples 29 to 56 according to the present invention had a higherwear resistance than the surface-coated cutting tools of ComparativeExamples 8 to 14, demonstrating that the tool life was improved.

While embodiments and examples of the present invention have beendescribed above, it is intended from the beginning that theconfigurations of the above embodiments and examples be appropriatelycombined.

The embodiments and examples disclosed herein should be construed asillustrative, rather than as limiting, in all respects. The scope of thepresent invention is defined by the claims, rather than by the abovedescription, and it is intended that all modifications within themeaning and scope of the claims and equivalents thereof be included.

1. A surface-coated cutting tool comprising a substrate and a coatingformed on the substrate, wherein: the coating is formed by physicalvapor deposition and includes one or more layers; at least one of theone or more layers is a first coating layer; and the first coating layercontains aluminum and nitrogen, has a thermal effusivity of 2,000 to5,000 J·sec^(−1/2)·m⁻²·K⁻¹, has a thickness of 0.2 to 5 μm, and has acrystal structure including a hexagonal structure.
 2. The surface-coatedcutting tool according to claim 1, wherein the first coating layer is anoutermost layer of the coating.
 3. The surface-coated cutting toolaccording to claim 1, wherein the first coating layer has a hardness of2,500 to 3,800 mgf/μm2.
 4. The surface-coated cutting tool according toclaim 1, wherein the first coating layer has a residual stress of −1 to0 GPa.
 5. The surface-coated cutting tool according to claim 1, whereinthe first coating layer is formed by sputtering.
 6. The surface-coatedcutting tool according to claim 1, wherein the first coating layercomprises Al_(1-x)Me_(x)N (0.001≦x≦0.2), where Me is one or moreelements selected from the group consisting of vanadium, chromium,yttrium, niobium, hafnium, tantalum, boron, and silicon.
 7. Thesurface-coated cutting tool according to claim 1, wherein the coatingincludes one or more second coating layers in addition to the firstcoating layer, the second coating layers comprising one or more elementsselected from the group consisting of group IVa, Va, and VIa elements ofthe periodic table, aluminum, and silicon, or a compound of one or moreof the elements with one or more elements selected from the groupconsisting of carbon, nitrogen, oxygen, and boron.
 8. The surface-coatedcutting tool according to claim 7, wherein one or more of the secondcoating layers comprise one or more elements selected from the groupconsisting of chromium, aluminum, titanium, and silicon or a compound ofone or more of the elements with one or more elements selected from thegroup consisting of carbon, nitrogen, oxygen, and boron.
 9. Thesurface-coated cutting tool according to claim 7, wherein the secondcoating layers have a supermultilayer structure including periodicallystacked thin-film layers having a thickness of 1 to 100 nm, thethin-film layers comprising one or more elements selected from the groupconsisting of chromium, aluminum, titanium, and silicon or a compound ofone or more of the elements with one or more elements selected from thegroup consisting of carbon, nitrogen, oxygen, and boron.
 10. Thesurface-coated cutting tool according to claim 1, wherein the substratecomprises a cemented carbide, a cermet, a sintered cubic boron nitridecompact, a high-speed steel, a ceramic, or a sintered diamond compact.11. The surface-coated cutting tool according to claim 2, wherein thefirst coating layer has a hardness of 2,500 to 3,800 mgf/μm2.
 12. Thesurface-coated cutting tool according to claim 2, wherein the firstcoating layer has a residual stress of −1 to 0 GPa.
 13. Thesurface-coated cutting tool according to claim 3, wherein the firstcoating layer has a residual stress of −1 to 0 GPa.
 14. Thesurface-coated cutting tool according to claim 2, wherein the firstcoating layer is formed by sputtering.
 15. The surface-coated cuttingtool according to claim 3, wherein the first coating layer is formed bysputtering.
 16. The surface-coated cutting tool according to claim 2,wherein the first coating layer comprises Al_(1-x)Me_(x)N (0.001≦x≦0.2),where Me is one or more elements selected from the group consisting ofvanadium, chromium, yttrium, niobium, hafnium, tantalum, boron, andsilicon.
 17. The surface-coated cutting tool according to claim 2,wherein the coating includes one or more second coating layers inaddition to the first coating layer, the second coating layerscomprising one or more elements selected from the group consisting ofgroup IVa, Va, and VIa elements of the periodic table, aluminum, andsilicon, or a compound of one or more of the elements with one or moreelements selected from the group consisting of carbon, nitrogen, oxygen,and boron.
 18. The surface-coated cutting tool according to claim 17,wherein one or more of the second coating layers comprise one or moreelements selected from the group consisting of chromium, aluminum,titanium, and silicon or a compound of one or more of the elements withone or more elements selected from the group consisting of carbon,nitrogen, oxygen, and boron.
 19. The surface-coated cutting toolaccording to claim 18, wherein the second coating layers have asupermultilayer structure including periodically stacked thin-filmlayers having a thickness of 1 to 100 nm, the thin-film layerscomprising one or more elements selected from the group consisting ofchromium, aluminum, titanium, and silicon or a compound of one or moreof the elements with one or more elements selected from the groupconsisting of carbon, nitrogen, oxygen, and boron.
 20. Thesurface-coated cutting tool according to claim 2, wherein the substratecomprises a cemented carbide, a cermet, a sintered cubic boron nitridecompact, a high-speed steel, a ceramic, or a sintered diamond compact.